Structures of the C8H6+ cation formed upon loss of acetylene from ionized naphthalene

Ionized naphthalene undergoes unimolecular loss of acetylene in the gas pha se, which leads to the formation of a C8H6+ species of hitherto unknown str uctures. In order to possibly afford different isomers, C8H6+ is generated using several precursors, i.e., naphthalene, azulene, 1-chlorobenzocyclobut ene, benzocyclobuten-2-ol, 1,2-di(bromomethyl)benzene, phenylacetylene, 2,4 ,6-octatriyne, 2,7-dichloro-3,5-octadiyne, and 1,3,5,7-cyclooctatetraene. M ass-selected C8H6+ ions are investigated by different mass spectrometric te chniques, such as collisional activation (CA), neutralization reionization (NR), and charge reversal (CR). Charge reversal of cations;to anions is mos t informative and yields structurally indicative fragmentations, which are much less pronounced with the other techniques. Comparison of the CR spectr a of the C8H6+ cations disputes the formation of ionized phenylacetylene an d 2,4,6-octatriyne upon loss of acetylene from naphthalene ion. Further, fo rmation of ionized cycloocta-1,3,5-triene-7-yne can be ruled out by compari son with the data obtained for the corresponding anionic species. While the experimental results are in accord with the formation of ionized benzocycl obutadiene upon loss of acetylene from naphthalene ion, other isomers which have not been considered previously may also represent likely candidates.